53^ 



SCIENTIFIC NEWS. 



[June 8, lE 



phor moves as it does upon water. 'It is not necessary 

 for this purpose that the mercury should be purified 

 with extreme care. It may be skimmed from dust, etc., by 

 passing over it once or twice a slip of very clean glass. On 

 sprinkling over it a few granules of camphor, and forming 

 a haze on the surface with the breath, we observe a 

 multitude of objects like long-tailed tadpoles, of extreme 

 agility, moving on the surface of the mercurj'. Each is 

 formed by a spot, a trace of the vapours in the midst of 

 the haze which leaves the mercury bare. This experi- 

 ment, which is very easy, is shown in Fig. 3. 



It is possible to demonstrate, for mercury as well as 

 for water, that the movement is due to a difference of 

 surface-tension. To prove this experimentally it is 

 merely necessary to blow gently from one side in a con- 

 tinuous manner upon the surface of the mercury. The 

 tadpoles, if we may so call them, flock in the direction 

 contrary to the blast, and collect on the convex margin of 

 the mercury nearest the observer. The movements are 

 more lively if the mercury is slightly vi?armed. The 

 same thing may be observed with naphthaUne. 



The experiment can be performed upon water, though 

 the success is not so certain. The material used is burn- 

 ing flower of brimstone, scattered upon the water. It 

 displays there capricious movements analogous to those 

 of camphor. Upon blowing the flame grows more 

 active, and a fragment often moves against a violent 

 current of air up to the edge of the vessel. The observa- 

 tion is here the more striking, as the wind carries along 

 all other floating particles. 



We now know the cause of the movements of the 

 camphor, but we know nothing as yet of the mechanism 

 of their stoppage. It appears, however, from the experi- 

 ments of MM. Joly and Boisgiraud, that this stoppage 

 takes place whenever a fatty pellicle, however slender, 

 exists on the surface of the water. 



It seems very natural to attribute the stoppage to a 

 decrease of the surface tension. An analogous experi- 

 ment is demonstrative of this effect : place upon very 

 pure water a ring formed of flexible thread, waxed. It 

 is irregular in its outline, but if aSdrop of oil be placed 

 within it, it suddenly changes into a circle which the oil 

 does not pass. If placed outside, the drop of oil pro- 

 duces the opposite effect, the ring contracting into folds as 

 close as the flexibility of the thread permits. These two 

 effects follow from the fact that the wire is in each case 

 drawn towards the surface which is free, and which has 

 consequently retained all its force. This shows that the 

 oil reduces the surface-tension of the water. 



But another factor must be considered, viscosity. It is 

 so great that we may see the oily layer move as a whole 

 with all that it contains. To separate these two causes 

 of stoppage, viscosity and reduction of surface-tension, 

 M. Devaux has connected, by means of a rigid bridge, 

 two identical boats, one placed upon an oily surface and 

 the other on a surface of pure water. A floating ring of 

 brass wire, varnished, is first placed upon very pure 

 water, and the connection between the two boats is then 

 fixed astride of the ring. A fragment of camphor placed at 

 the stern of the outer boat sets the whole in motion. A 

 drop of oil is then placed in the inner circle and the 

 movement continues, being scarcely slackened. It is 

 observed, however, that from this moment the ring is 

 also manifestly carried along. Thus the viscosity of the 

 oil does not suffice to explain the stoppage of the move- 

 ments of the camphor. The change of the surface ten- 

 sion is the sole important factor. 



As a further refutation of the theory of a reaction, 

 M. Devaux places upon water, whether oily or not, a 

 large float in the form of a watch-glass, and the boat is 

 placed close to its edge (Fig. 4). The movement con- 

 tinues, though of course slackened. Upon the float he 

 places any object, so that the total weight to be moved 

 may reach 50 or 100 grammes, or even a kilo. ; the 

 movement continues. If it be stopped it quickly begins 

 to move again. 



If we think of the friction overcome and the mass 

 carried round, we must admit that the current produced 

 by the emission of less than i-5oth of a cubic millimeter 

 of vapour per minute is unequal to such efiects, for it 

 would be necessary to ascribe to the particles emitted a 

 sudden velocity of 70 kilometres per second. 



From these experiments it may be concluded that the 

 cause of the movements of camphor upon mercury is 

 now explained and found to be a known and measurable 

 force. 



The question of the action of oil upon the waves of 

 the sea may, perhaps, be usefully taken in hand from 

 this side. 



NOTES ON ESSENTIAL OILS. 



A NISE oil is now almost wholly produced in Russia. 

 Camphor oil, from Japan, is coming into favour as 

 a solvent for resins, paraffines, stearin, etc. In Japan 

 it is coming into use as a solvent in lacquers. A 

 favourite lacquer consists of camphor oil, 10 parts; oil 

 of turpentine, 35 parts ; and copal resin, 8 parts. 

 Paper treated with a solution of common resin in 

 camphor oil becomes very transparent. A lacquer for 

 metals is made by mixing camphor oil, 22 parts, with 

 melted asphalt, 5 parts. Paper may be rendered water- 

 proof by treating with a mixture of camphor oil and 

 linseed oil. 



Cananga oil, designated as Indian, imported from Java, 

 is supposed to be derived from the same plant as that 

 which furnishes the ylang-ylang oil of the Philippines, 

 but it is sold at a much lower price, and is very inferior 

 in odour. 



Cedar-wood oil, used largely in Germany as a basis 

 for soap perfume, is obtained chiefly from the waste of 

 the lead-pencil industry. 



Eucalyptus oil, from E. globulus, is now produced in 

 California in large quantities as a by-product in the 

 manufacture of a preparation to prevent incrustations in 

 steam boilers. Algeria also competes with Australia in 

 the production of this oil, and is able to supply all 

 present demands. The manufacture of the oil in Australia 

 is, however, increasing, and a plant is about to be estab- 

 lished also in Tasmania for distilling it. The statement 

 that the oil of E. amygdalina contains no eucalyptol is 

 reaffirmed. The product sold as eucalyptol derived from 

 the last-named species differs in toto from true eucalyptol. 

 The former consists of a mixture of a terpene (eucalypten, 

 C,o H,^) with a little cymol, and is distinguished at once 

 by its low specific gravity, o-886 at 15° C, the 

 genuine article having a sp. gr. of o'930. 



Turkish geranium oil (Palmarosa oil), more properly 

 called Andropogon oil, is said to be submitted to a 

 special treatment to render it suitable for use in adul- 

 terating oil of rose. It is bleached in the sun and 

 rectified several times over rose leaves. 



